significant effects on genetic diversity and evolutionary potential. The effects of bottlenecks on the diversity of symbiotic partners of plants, such as rhizobial bacteria and mycorrhizal fungi, are little studied. We are exploring the effects of plant population bottlenecks in a variety of contexts, from domestication and breeding in crop plants; to declines in population size due to habitat loss, fragmentation, and degradation in endangered species; to bottlenecks that result from introduction to a new range in introduced and potentially invasive species. In cultivated crops and invasive species the absence of co-evolved or co-adapted symbiotic partners in a new range may select for greater partner breadth and less dependence on microbial symbionts. For microbial partners, new potential hosts may shift patterns of host association and lead to rapid shifts in networks of interactions. With declining species, host and microbial symbiont may both face risks of an extinction vortex. Examples are highlighted from ongoing work on partner choice in chickpea and its wild relatives, and rare and invasive legumes of habitats threatened by sea level rise in South Florida. In all the plants have undergone strong bottlenecks. Symbionts,with larger population sizes, are less prone to bottlenecks.